Insignia TV won't turn on

[KilgoreCemetery]

I'm a bit of a noob at this, but I have the back of the tv off and have been checking the PCB with a multimeter. The problem is that a lot of the readings fluctuate as I'm reading them. Is this a common issue with a common cause or is it something I have to track down? I have no idea what this indicates. Where do I go from here?

 

[shrtrnd]

It would probably help us to help you if you list the model number on the back of the TV, maybe we can find a schematic for it to give you an idea of where to look.
The most obvious thing we'd check first however, are any fuses inside the television.
Unplug the set from the wall. Look inside for any fuses, remove the fuse and use your multimeter on the resistance function to check for continuity.
The second most obvious thing any of us would do, is with the TV unplugged, physically look at the components on
the printed circuit boards for any obvious physical damage, or evidence of overheating.
That should keep you busy until somebody here finds a schematic for your set.
You know the set is not working. Don't plug it in again until you check the above items first.

 

[KilgoreCemetery]

Thanks for the reply, shrtrnd. The model number of the TV is NS-32D201NA14. Not sure which of the numbers is for the model of the power board, but maybe 6MY00320C0 or 569ME2320.

The only fuse I see looks like an electrolytic capacitor, but is labeled FUS01 on the circuit board. It is reading zero ohms, but do I need to actually remove it from the circuit board to test it or is that good enough for now?

Also, I did give the power board a good look over (front and back) and there are no obvious signs of damage. No black spots and all the capacitors are flat on the top.

Something that I forgot to mention before, though, is that some times I could hear a quiet buzzing noise from the power board when it was plugged in. It seemed to oscillate a bit and appeared to be in time with the voltage fluctuations.

The TV is currently turned off and unplugged.

 

[shrtrnd]

A board marking that says 'FUS' is very likely a fuse.
Zero ohms across it sounds promising, but your meter is also reading the rest of the circuit in-line with the fuse.
To check a fuse, it really should be removed and checked alone.
'Buzzing' sounds at low volume are not all that unusual (though it could indicate a problem).
Most TV's used to have only one fuse, but some of the newer ones have more than one. Do you see any
other 'FUS' markings on the boards?
Does your set have a manual on/off push-button on the set, or just the remote (just asking to make sure your
set actually isn't turning on, and that you just don't have a problem with the remote if that's all you've tried so far)
I don't have time to look-up your schematic right now, hopefully somebody will get back to you soon if I can't.
What we'll be recommending that you do, is step-through the input power stages of your power supply, to try to
find-out where the problem is, it's usually the power supply.
The issue for us, as you are a noob, is do you feel knowledgeable enough about electronic circuits to make troubleshooting tests, or do you know somebody who is? We don't want you to hurt yourself with high voltage
if you try to troubleshoot this problem yourself.

 

[KilgoreCemetery]

Ok, I'll pull out the fuse and check it properly. It's the only one on that particular board, but there are three boards all together and I'll pull and test any fuses I find on them too.

I have been using the manual on/off button on the TV itself to rule out a remote problem.

As for my knowledge base, I am a quick study and youtube videos and tutorials have gotten me quite a ways already, but some times they aren't the best at actually walking you through something unless you're both working on the exact same project.

I have already verified that the power cord itself is providing 120vdc to the power board, though. I'm just lost as to what to do from there.

Here's an actual photo of the power board, if that helps.

 

[73's de Edd]

Sir "Kilgore" . . . . . .


That set uses a special lag time electro chemical fuse.

Its module location is left corner, just right to the side of the white Molex AC line connector

It says CAUTION . . . . LIVE AREA, but in your area, that probably is not the norm, or they wouldn’t be there.

It’s reddish brown color . . .NOW YELLOW circled, a round cylinder and designated as ? F? 001 . . . of all that I can make out.

BUT the smart, fuller testing is to completely reinstall the board and connect up and do a voltage test..

Note the two black 150 ufd / 200V cylindrical electrolytic capacitors just in the area above.
Polarity is being further marked up for you.

After power turn on

Use DC metering in the ~200 VDC range to measure across the + and – leads of one filter then the other expecting ~ 160-170 VDC from each . . . if so . . . yo’ fuze iz gud ! . . . plus a whole STRING of intermediate parts.

Go to 500 VDC range and do a quick touch test to see what the voltage read is from the extreme right - term of the right cap to the extreme left + terminal of the left cap is.

As they just might be voltage doubling . . Put that voltage reading in your pocket and carry it back with you.

We now leave you, to go demonstrate your first degree of techno prowess.

http://i.imgur.com/MIJguCG.jpg

73's de Edd

 

[KilgoreCemetery]

Thanks for the info, 73's de Edd. The board is now fully reinstalled and each of the capacitors does, indeed, show roughly 165vdc. Probing from the far left (positive) side of one cap to the far right (negative) side of the other cap only shows about the same 165vdc though.

 

[KilgoreCemetery]

I did also pull the fuse on the power board and it tested fine. There are no other fuses that I can find inside the TV

 

[KilgoreCemetery]

I removed the power board and traced some of the fluctuating voltages. On the bottom of the board there is a small IC with "MP4012" on it. I was able to find a data sheet for it and wrote down some voltages. I feel like someone smarter than I can figure out if the values I'm seeing indicate whether the chip is working properly or not. (Data Sheet included below)

1) 12.46V Vin
2) 7.64V Vdd
3) *fluctuates* Gate
4) -7.4mV GND
5) -7.5mV CS
6) -6.9 to -7.1mV SL
7) 6.51V RT
8) 7.62V SYNC

9) 295.2mV CL
10) 1.231V REF
11) -7.mV FAULT
12) 3.78V OVP
13) 1.57V PWM
14) 7.61V COMP
15) 0.499V ISET
16) -7.3mV FB

 

[KilgoreCemetery]

Still researching this. Things I've learned today: The two little ICs that are located by the MP4012 mentioned previously are MOSFETs. I was able to find a datasheet for the first one, SM2A04NSU, but nothing for the second one. It has EMBJON25 on one line and AFF2402 on the other. I wonder if it's similar to an IRLML2402, but this one is a 4-pin chip. The major downside is I have zero information for this chip, but it directly feeds into a connector pin labeled LED2-. The reason this seems so important is 1) the voltage for that pin constantly fluctuates, and 2) The plug for that connector goes right into the back of the TV. I am assuming that this controls the LED backlight, but I'm not sure. I'm also wondering if maybe the voltage for this is actually supposed to fluctuate.. not sure.

 

[KilgoreCemetery]

Meanwhile, on another part of the Power Board, I've been testing a 6-pin connector that goes to the Main Board. It has two pins dedicated to 12V, two labeled Ground, one BON (button on?), and one PWM (Pulse Width Modulation?). The important part is that none of the readings for these pins fluctuate at all. This is what it looks like when the TV is on:

BON: 5V
PWM: 2.5V
Ground:
Ground:
12V: 12.47V
12V: 12.47V


I've determined that the two 12V rails are active all the time so they must supply power over to the Main Board, which is, in turn, supplying power to the On/Off switch. When the switch is activated it must be sending power back over the BON pin (I'm guessing), through some tiny resistors, and down to the previously mentioned LED controller MP4012. This appears to be the first place that the voltage fluctuation appears. Pin 3 of the chip, labeled GATE, has a power output that I would imagine looks like a sawtooth pattern on an oscilloscope (pure speculation by an idiot here).

From there it seems to go all over the place. One path, in particular, goes through the SM2A04NSU MOSFET that I have the data sheet for and continues over to the other MOSFET that I know nothing about, which feeds the LED2- Pin. Then it's over the hills and through the woods, to Grandmother's house we go.

However, the big question is should the GATE pin of the IC be fluctuating in the first place???

 

[73's de Edd]

Sir "Kilgore" . . . . . .


I was just about to ask for as good of a photo as my post # 6 is providing, but being shot of the FOIL side of the board.

I initially got with you as far as the main filter capacitors and their having the required 165 VDC out from them.

Brief Operational Synopsis:

That voltage then feeds up to the LARGE cored YELLOW transformer with the power device associated with it, being the power FET to its left, peeking out of the right edge of its heat sink, you can see it as V501 device marking and its Drain-Source-Gate leads.

There is one 14 or 16 pin surface mount IC, other side of the board, which feeds gate drive to it.

It is working, as your transformer is operating and feeding power output to D511 and its companion just below it to create your 12VDC, which gets filtering by the cluster of elect caps above them.

White X503 connector below, has its Board ON—Pulse Width Modulation ---Gnd---Gnd--- 12VDC---12VDC pins..

Now we drop down to the boards right bottom quadrant, where the LED backlight clusters supply is.
There is where you found your driver IC and its associative power FET, on the foil s ide of the board.

You probably have either an overload or loss of some series LEDs in a strip causing your power cycling from this section.

Since I am working totally nekkid . . .. without a schematic, I need the foil side photo to “ read it “ .

In the interim, I need some measurements from the ohms function of your DVM.

NO power on the set for this testing.

Metering set to ohms function lowest range.

Short the meter probes and see how your meter display reads out a short / direct connection.

Open the probes to then see how an open circuit is displayed.

Let’s just initially see all of the commonly grounded connections.

Extreme top right corner is the ground lug eyelet that gets chassis grounded by its mounting screw thru it.

Measure from there to both Gnds on X503 connector. Being Connected ? Expecting so.

Then keep one lead at the ground eyelet and confirm a direct connection to the neg terminal of the nearby C520 elect . Being Connected ? Expecting so.

Check for a direct connection to the – term of the lower left C618 elect. Being Connected ? Expecting so.

Check for a direct connection to the lower right white X601 connectors #3 far right LED connector pin. Expecting so.

This would be all expected common shared grounds.

Now back to the two large diodes to the right of the transformer.

The question is if they are used as a shared pair in getting your 12VDC over to the right X503 connector.

To confirm that, ohm between the silver banded ends of those 2 diodes. If they are connected both are creating your 12VDC.

HOWEVER . . . I suspicion that the bottom diode provides another supply, with it receiving its power from a higher voltage output winding of the transformer.

That voltage then gets initially filtered by C520 . . . and we can expect that voltage to be less than 100v.

The voltage then passes thru heavy ferrite based inductors L601 and L602 which may only provide passive RFI isolation filtering OR they might be active element(s) in an inductive kick back / ringing power supply, utilizing your back board find of the MP4012 switch mode driver IC which drives a SM2A04NSU power MOSFET(s).

Prepare to measure some voltages now, as you did on your last power ups.

Your readings have confirmed a constant 5VDC standby supply and a steady 12VDC supply as derived from your units central transformer. All is well there.

Measure across C520 to see what that peak DC voltage is, and if it is going up and down at the rate experienced on your MOSFET’s gate drive.

Move down and measure across C618 elect and see what is happening there, then probably the flow path is thru ferrite inductor lead L604 over to the X601 pin 1 LED +.

Our main interest being . . . in voltage levels and fluctuations.


Thassssit


73’s de Edd

 

[KilgoreCemetery]

Thanks for the reply, 73’s de Edd!

Let's start with the easy stuff. Here's new pictures of the board, front and back, with a clip in one corner for orientation reference. I'm off to record measurements. Be back in a short bit.

 

[KilgoreCemetery]

Ok, I think I've got everything.

It's an auto-ranging multimeter, but touching the two leads together shows 0.0 ohms.

Open circuit is displayed as 0.L

Ground eyelet to X503 grounds: 0.1 - 0.2 ohms, which is what my meter normally reads for "good connection"

Eyelet to C520: 0.1ohms

Eyelet to C618: 0.3ohms

Eyelet to X601: Far right pin is showing 0.L, so is center pin (which I don't think is actually connected to anything), and pin 1 is showing high resistance. It started with 0.L, then jumped into the 20M ohms range, then started climbing back down

The silver-banded ends of the two large diodes do the same thing as X601, pin 1.

________________Powered on the TV________________

Everything that fluctuates seems to do it at the same speed. About 3.5s per cycle

Standby Readings
C520 54.7V
C618 54.7V

X601, pin 1: 54.5V
X601, pin 3: 12.65V

Power On Readings
C520 63 - 66V
C618 80 - 85V

X601, pin 1: 80 - 85V
X601, pin 3: 35 - 38V with a brief reading of 57V. Could just be a misread by the meter. Readings change pretty quick.

Eyelet to D511: -8.7mV -> 12.47V This is the only one of these readings that doesn't fluctuate while the TV is on
Eyelet to D509: -8.7mV -> 63 - 66V

 

[73's de Edd]

Sir "Kilgore" . . . . . .

Initially . . . I'm sure that our . . . . . R.H.R&E DAVENN will LIKE this:

Now . . .like Dirty Harry . . . I just gots to knows !. . . . is that cat in your Avatar a flying Ninja or Kung Fu kitty . . .or . . . .alas . . . . just one walking upon plate glass ?

Stil looking in the DEEEEEP bushes for a proper schematic of your INSIGNIA 32 inch LCD Tee Wee.

It possibly being a Best Buy ( or was it Circuit City) closeout special . . .I'm thinking the former.
BUT this unit is bastardized, by its also showing up marketed under four or more other brands like:
Durex, Hisense, ATV (Asian TV) . . . I found a Hisense that is using the same parts numbering assignments, with the 500 series reserved for the power supply components and the 600 for the LED backlight related circuitry.

After your measurements and feedback . . . .
What I really think the problem on your set is:

That there is one LED opened up on a series string of one long strip panel and there may be 5 or more strip panels spaced apart behind the screen.
On the Hisense I saw that the white connector X601 with its LED1 and LED2 ibelieve . . . (as I can only see the D01 and D02) . . . feeds your backlight strips.

BTW I just now saw that you DID provide me with the foil path side of the board and it's being VEWY-VEWY G-O-O-O-O-O-D !..

I will get back with a prep up of the HISENSE schema so you can check the components tied into the LED1 and LED2 connector.

On that schema I see two strings of high value resistors series strung out on both sides and they are sampling both legs for voltage . If a strip is dead, that would INCREASE that voltage being tested at that point and causing the repetetive:
1 Start up and supply voltage to the LEDS
2 Sample voltage present
3 OH MY . . . . . IT's TOO HIGH !
4 Shut down and start up again..

Over and over again.

73's de Edd

 

[davenn]

great info, Edd

 

[KilgoreCemetery]

Wow, that sounds like a solid lead, Edd.

Also, aren't all cats flying Kung Fu ninja kitties?